Refactor SD detect handler (#17380)

Co-Authored-By: Eric Ptak <trouch@users.noreply.github.com>

Marlin/src/sd/cardreader.h

@@ -73,6 +73,9 @@ public:
   static inline bool isMounted() { return flag.mounted; }
   static void ls();
 
+  // Handle media insert/remove
+  static void manage_media();
+
   // SD Card Logging
   static void openLogFile(char * const path);
   static void write_command(char * const buf);